1. Field of the Invention
The present invention relates to a structure of a transmission comprising a belt-type continuously variable transmission (hereafter referred to as xe2x80x98CVTxe2x80x99), which is suitable for a working vehicle.
2. Background Art
A conventional working vehicle, e.g., a truck, includes a belt-type CVT connecting an output shaft of an engine and an input shaft of the transmission such that rotation of the output shaft of the engine is transmitted to its axles and drives them. In this vehicle structure, a sensing mechanism is provided at the CVT and detects rotary speed or load of the engine so as to automatically steplessly reduce/increase the speed reduction ratio according to the increase/decrease of rotary speed of the engine or the decrease/increase of the engine load.
In addition, it is well-known to laterally mount an engine on a vehicle so as to locate its crankshaft perpendicular to the longitudinal direction of the vehicle and in parallel to an input shaft of a transmission, an output shaft of the transmission, and axles. This described vehicle structure especially facilitates interposing a belt-type CVT between the crankshaft of the engine and the input shaft of the transmission because both shafts are parallel to each other. Moreover, the transmission in this vehicle structure may transmit power via economical spur wheels because shafts therein are disposed parallel to one another. Therefore, the vehicle structure is advantageous in contributing to the reduction of assembly and material costs.
An object of the invention is to provide a transmission for a working vehicle that is simplified so that the manufacturing costs can be more and more reduced.
Further, conventional transmissions with differential locking mechanisms provide a shaft for operating the differential locking mechanism that is axially, slidably supported and is disposed parallel to the axles. The differential locking slider is engaged with a fork fixed onto the shaft so as to slide the differential locking slider integrally with the shaft, thereby switching between a differential-locking mode and a differential-unlocking mode.
However, in the above conventional structure, the fork engaged with the differential locking slider is apt to be large, thereby inhibiting miniaturization of the transmission. And, because a space inside of the transmission housing is required for straightly moving such a large fork back and forth at a set stroke to operate the differential locking slider, further miniaturization of the transmission is difficult.
The transmission of the present invention is applied to a working vehicle having an engine mounted on a bodywork frame such that a crankshaft of the engine is disposed horizontal to the ground and is perpendicular to the longitudinal direction of the vehicle. The transmission comprises an input shaft for receiving power of the engine through a CVT, an output shaft disposed in parallel with the input shaft, a pair of left and right axles aligned with and extending out opposite to each other and in parallel with the output shaft, a differential connecting the left and right axles with each other in a differential manner, a transmission housing containing the differential, a pair of left and right axle housings mounted onto left and right faces of the transmission housing respectively, each of which houses each of the pair of axles, having mounting portions for mounting to the bodywork frame, and a wet-type disc brake device provided around a portion of the axles covered by the axle housings. Therefore, a load, which is applied to drive wheels fixed on the axles, can be supported by the transmission housing through the axle housings, thereby simplifying the structure of a vehicle. And, in comparison with the conventional structure having an output of a differential that is transmitted to the drive wheels through universal joints and a dry-type brake device, manufacturing costs can be reduced. Furthermore, due to the wet type disc brake device, durability and reliability of the brake device can be improved.
The input shaft is disposed closer to the engine than said axles in the longitudinal direction of the vehicle. Therefore, the position of the input shaft, while keeping a required distance from the axles, can be lower than that when being above the axles. Due to this arrangement, even if the amount of lubricating oil in the transmission housing is small, splash lubrication for the input shaft can be sufficient. Consequently, the amount of lubricating oil can be saved, thereby reducing manufacturing costs and weight of the transmission. And, when the present invention is applied to a transmission of a truck, its deck can be located at a low position, thereby improving capacity of the deck and sinking the center of gravity of the truck.
The transmission further comprises a drive train which can switch the rotational direction of the output shaft in relation to the rotational direction of the input shaft, wherein the drive train drivingly connects the input shaft with a portion of the output shaft, which is nearer to one end of the output shaft, a prime rotary object provided on the output shaft nearer to other end of the output shaft, a follower rotary object serving as an input means of said differential, the follower rotary object being engaged with the prime rotary object, and a centrifugal governor for changing the output of the engine according to the variation of the rotational speed of the input shaft, the centrifugal governor being disposed at a portion of the input shaft facing toward the prime rotary object. Therefore, by the adoption of the centrifugal governor which is smaller and less expensive than a torque governor, manufacturing costs of the transmission can be saved and compactness thereof can be improved. And, because the centrifugal governor is placed at empty space inside of the transmission housing, a layout of the transmission can be simple and space-saving, thereby further improving compactness of the transmission.
The transmission further comprises a pair of left and right transmission housing parts into which the transmission housing is laterally dividable through a surface which is perpendicular to a longitudinal direction of said axles, wherein the differential is supported at its left and right portions by the left and right transmission housing parts, respectively, and bearings provided at outer ends of the respective axle housings, wherein the bearings support outward portions of the axles projecting leftward and rightward from the differential. Therefore, because the differential can be directly supported by the transmission housing without intervention of the axles, when manufacturing of the transmission, a convenient assembling method (i.e., a method of putting in axles after fixing the differential to the transmission housing by joining together of left and right housing parts) can be adopted. Furthermore, since outward portions of the axles are supported by the axle housings through the bearings, the weight of the vehicle can be surely supported by the axles through the axle housings.
A portion of at least one of said the housings to be attached to the transmission housing is expanded so as to be bowl-like shaped. The wet-type disc brake is disposed in the bowl-like shaped portion of the axle housing, and an arm for operating the wet-type disc brake is disposed outside the bowl-like shaped portion of the axle housing. Therefore, because a room which houses the wet-type disc brake (i.e. the bowl-like shaped portion) is integrally formed with the axle housing, manufacturing costs of the transmission can be reduced. And, because the arm for operating the wet-type disc brake is disposed outside the bowl portion of the axle housing, the operating system from the arm to wet-type disc brake can be compactly and simply formed.
A transmission of a working vehicle comprises a differential, a transmission housing containing the differential, a pair of left and right axles connected with each other in a differential manner by the differential, an axle housing mounted onto one of left and right faces of the transmission housings to support one of the axles, wherein a joint space is formed in a joint portion between the transmission housing and the axle housing, a differential locking slider which can switch between a differential mode for connecting the left and right axles with each other in a differential manner and a differential-locking mode for integrally connecting the axles, a friction disc provided on the axle supported by the axle housing, and a pressure member which pushes the friction disc so as to brake the axle, wherein the pressure member and the differential locking slider are disposed substantially coaxially with each other in the joint space. Therefore, the differential locking slider and the pressure member can be arranged in a compact length of longitudinal direction of the axles, thereby contributing to space-saving of the transmission.
A guide portion for axially slidably supporting said pressure member is provided in a flanged portion formed on an outer side wall of the transmission housing for mounting the axle housing, the differential locking slider is disposed in the guide portion, and a round wall of the guide portion is partly notched such that an arm for operating the differential locking slider is inserted through the notched portion. Therefore, because the pressure member is supported by the guide portion and the differential locking slider is located inside of the guide portion, both of them can be apportioned between inside and outside of the guide portion in a compact mass. And, because the round wall of the guide portion is partly notched and the arm for operating the differential locking slider is inserted through the notched portion, the simple structure for operating the differential locking slider located in the guide portion from the outside of the guide portion can be achieved.
The pressure member is rotatable along said round wall of said guide portion by a brake operating shaft supported by said axle housing, and a cam body, which thrusts the pressure member in correspondence to as rotational degree of the pressure member, is supported around the round wall of the guide portion. Therefore, since the pressure member rotates while it is guided by an outer peripheral surface of the round wall of the guide portion, a special structure for axial alignment of the pressure member can be eliminated. And, since the cam body is supported around the round wall of the guide portion, the compact structure that the pressure member pushes the friction discs by axially sliding while rotating can be achieved.
A rotational axis of the arm for operating the differential locking slider is disposed at a position which is offset from a virtual plane containing the rotational axis of said pressure member, and the brake operating shaft is placed in parallel with the axles on a opposite side to the arm with the virtual plane between. Therefore, an operating system of the differential locking slider and an operating system of the brake device can be compactly arranged and can avoid interruptions with each other, thereby miniaturizing the transmission.
Furthermore, the transmission further comprises an input shaft projecting outward from one of left and right sides of said transmission housing and a follower pulley constituting a belt-type CVT disposed onto an outward projecting portion of the input shaft, wherein said differential locking slider is disposed at a position nearer to the other of the left and right sides of the transmission housing. Therefore, an operating system of the differential locking slider can be disposed in a position wherein the operating system can avoid interruptions with the CVT, thereby improving the compactness of the transmission.